This invention relates to a non-aqueous fluidized polymer suspension for use as a rheology modifier in paper coatings. More particularly, this invention is directed to the use of an environmentally acceptable fluidized polymer suspension of carboxymethylcellulose in a light white mineral oil for use in paper coating applications.
Carboxymethylcellulose (CMC) is well known for its industrial use in paper coatings. CMC has been used in its dry form as a direct additive for paper coating formulations, although this usage has mainly been limited in the past to low molecular weight, i.e., low viscosity, CMC types. This limitation is due to the fact that higher molecular weight CMC dry powder tends to form lumps that are problematic to dissolve when added to paper coatings. In fact, even lower molecular weight CMC powder can form lumps when added to paper coatings without special precautions. Also, another difficulty with dry powdered CMC handling is dusting that can cause health hazards such as slippery floors and respiratory problems due to breathing the polymer particles.
Hence, in order to overcome such problems with dry powdered CMC, the paper coating industry has in places adopted the use of CMC liquid suspensions dispersed in fatty acid organic liquid carrier. Other general standard practice in the coating industry is to use low molecular weight CMC first dissolved in water to form a base solution before it is incorporated into paper coatings.
The use of CMC powder to prepare dilute aqueous solutions also creates problems. One such problem of using CMC solutions is that first the polymer has to be properly dissolved in water. This procedure suffers the limitation in that it is labor intensive and time consuming and highly viscous aqueous CMC solutions are difficult to prepare, store, and handle. Another problem with CMC aqueous solutions is that there is a limitation on how much CMC can be dissolved into this solution due to excessive viscosity development. In addition, another problem with these aqueous solutions is that numerous undissolved gel lumps can often form due to the tendency of CMC to lump when added to dissolution water. These gel lumps has to be removed either by stirring for a prolonged period of time or by physically removing them before addition to the paper coating. Special mixing equipment sometimes has to be used in order to prepare concentrated CMC solutions in water because of the highly viscous nature of these solutions.
Because of the problems with dry powder and aqueous solutions of CMC, fluid polymer suspensions were developed and are currently being used commercially to deliver these polymers to paper coating compositions. The use of fatty acid liquid carrier as a vehicle for these suspensions was a significant improvement over prior art handling and performance of dry CMC for paper coatings thickening applications. However, the use of fatty acid as a CMC suspension medium has historically been problematic as well. The manufacture, transport, and application of CMC fluid polymer suspensions based upon fatty acid has proven to be difficult. Instability, high viscosity, marginal fluidity, and/or residue formation have been observed with these products. Furthermore, some of these fatty acid based CMC fluidized polymer suspensions or other suspensions of CMC have contained less environmentally favorable ingredients.
The pollution from paper making plants has reportedly endangered fish and plant life in bodies of water near papermills and may threaten the ecological balance of these systems. For this reason in the past few years, legal sanctions and environmental restrictions in the paper making industry have required changes in chemical usage in papermaking and coatings systems. In this category, water based fluid systems are most preferred assuming all chemicals contained in the fluid systems exhibit low toxicity and high biodegradability. The chemicals used in these fluid systems are regarded as separate components that should meet the environmental regulations for nonpolluting paper coating fluids.
In addition to the use of fatty acid as a carrier for fluid suspensions of CMC, other liquid carriers cited in the prior art include mineral oil, kerosene, diesel fuel, and glycols. These hydrocarbon-based solvents that are commercially available may not be acceptable environmentally by most of the paper industry.
U.S. Pat. No. 5,001,231 (J. Zapico) discloses an invert emulsion polysaccharide slurry for industrial use containing (1) diesel, mineral, or paraffin oil, (2) surfactant, (3) water, (4) organophilic clay, and (5) a polysaccharide (CMC is disclosed).
U.S. Pat. No. 5,151,131 (J. Burkhalter et al.) discloses an anhydrous fluidized polymer suspension for use as a liquid fluid loss control additive for an aqueous well cement composition containing (1) liquid hydrocarbon (e.g., kerosene, diesel oil, light white mineral oils, and aliphatic hydrocarbon oils), (2) surfactant, (3) organophilic clay, and (4) a hydrophilic polymer, e.g., CMC.
U.S. Pat. No. 5,096,490 (C. L. Burdick) discloses a fluid polymer suspension for use in paper coatings containing (1) at least one water soluble polymer such as CMC, dispersed and suspended in (2) a fatty acid, and (3) an organoclay stabilizing agent, and (4) an oil-in-water emulsifier.
U.S. patent application Ser. No. 09/717884 discloses an oil-based fluid polymer suspension for use in oil or gas well servicing fluids containing a) a hydrophilic polymer, b) an organophilic clay, c) a stabilizer, and d) a white medicinal oil that i) has a low viscosity, ii) has no aromatic content, iii) has a high flash point, iv) has a low pour point, v) is food contact approved, vi) is non-toxic, and vii) is biodegradable, whereby this FPS composition is environmentally acceptable for use in offshore oil field servicing fluids.
U.S. Pat. Nos. 5,494,509, 5,725,648, and 6,030,443 disclose paper coating compositions that use polysaccharides.
The present invention is directed to a paper coating composition comprising a pigment, a binder, water, other standard paper coating adjuvants, and a light white mineral oil-based fluidized polymer suspension composition for use as a rheology modifier in the paper coating comprising a hydrophilic polymer, an organophilic clay, a stabilizer and a specific type of light white mineral oil. The light white mineral oil component of the present invention must exhibit a relatively low viscosity, have low aromatic content, exhibit a relatively high flash point, exhibit a low pour point, be food-contact approved, be non-toxic, and be biodegradable, thereby rendering the complete FPS composition environmentally acceptable for use in paper coatings.